You can buy a ticket to Longjia Airport directly from the bus station. It's a highway bus from Dunhua to Changchun. Longjia Airport is on the way to Changchun. It's a long way from Jilin

Yanji sells tickets to Longjia Airport. You can take a bus from Yanji to Changchun once an hour. Then, he stops at a place close to the airport, and then a van picks you up and takes you directly to the airport. If the bus from Dunhua to Changchun doesn't stop at the airport, get off at the Changchun toll gate and take a taxi, it's not much money

If you can't, you can go into the city and take a bus to the airport for 20 yuan per person